1. Technical Field
The present invention relates to piezoelectric oscillators and methods for manufacturing the same.
2. Related Art
Tuning fork type 32 kHz quartz oscillators are used in oscillator sections of clock modules in clocks and information devices such as microcomputers in order to take advantage of the traditional design assets and their power saving property. However, the arm length of the tuning fork arm in the case of a tuning fork type 32 kHz quartz oscillator is several mm, and therefore the overall length including its package may amount to about 10 mm.
In recent years, instead of quart, piezoelectric oscillators having a driving section formed from a piezoelectric thin film sandwiched between upper and lower electrodes formed on a silicon substrate have been developed. As the structure of such piezoelectric oscillators, a beam type structure (see FIG. 1 of Japanese Laid-open patent application JP-A-2005-291858) and a tuning fork type structure equipped with two beams (see FIG. 1 of Japanese Laid-open patent application JP-A-2005-249395) are known. Even with such piezoelectric oscillators, the silicon substrate can only be made at most to a thickness of about 100 μm. Therefore, in order to obtain a resonance frequency in a several tens kHz band, the arm length of the beam needs to be several mm or greater, which may lead to a problem in that miniaturization of the clock module is difficult.